The present invention relates to a starter generator for an internal combustion engine that operates as an electric motor for starting the internal combustion engine when the internal combustion engine is started, and operates as a generator after the internal combustion engine is started.
A starter generator for an internal combustion engine is comprised of a rotating electric machine that includes a magnet rotor mounted to a crankshaft of the engine, and a stator having a polyphase armature coil wound around an armature core, and a driver provided between the armature coil of the rotating electric machine and a battery.
The driver is comprised of a bridge type switch circuit that performs a function of transferring phases where a drive current is flowed so as to rotate the rotor in a predetermined direction, and a rectifier circuit that rectifies an AC voltage induced in the armature coil to supply the AC voltage to the battery after the engine is started.
Generally, a bridge type full-wave rectifier circuit in which a diode forms each side of a bridge is used as a rectifier circuit. The switch circuit is constituted by a switch element connected in anti-parallel to each diode of the rectifier circuit.
As a power supply unit that uses a generator driven by the internal combustion engine to supply power at a commercial frequency to a load, a power supply unit is often used, that includes an AC/DC converter that converts an AC voltage output by the generator into a DC voltage, and an inverter that converts an output of the converter into an AC voltage. Such a power supply unit is known as an inverter generator.
When the starter generator as described above is used, the inverter generator can be comprised by adding an inverter that converts a voltage of the battery into an AC voltage, to an output side of the battery that is charged with an induced voltage of the armature coil through the rectifier circuit in the driver.
The inverter generator is used instead of a commercial power supply, and thus a rated output voltage of the inverter generator differs depending on countries. There are five types of rated voltages of commercial power supplies now used across the world: 100 V, 110 V, 120 V, 230 V, and 240 V (all of them are effective values). These voltages can be divided into a 100 V system (100 V, 110 V, 120 V) and a 200 V system (230 V and 240 V).
In a conventional inverter generator, two types of generators having winding specifications suitable, one for obtaining a rated voltage of the 100 V system, and the other for obtaining a rated voltage of the 200 V system, are prepared to obtain the voltage for each system. Specifically, for the 100 V system voltage, a generator is prepared, having winding specifications that allow generation of an AC voltage with a peak value (approximately 170 V) required for obtaining an AC voltage of 120 V in a maximum rated voltage (an effective value) in the system, and an output of the generator is once converted into a DC output, then the DC output is input to an inverter, and the inverter is controlled to generate the AC voltage of 100 V, 110 V, or 120 V, when the internal combustion engine is in a normal operation state.
For the 200 V system voltage, a generator is prepared, having winding specifications that allow generation of an AC voltage with a peak value (approximately 339 V) required for obtaining an AC voltage of 240 V in an effective value, and an output of the generator is once converted into a DC output, then the DC output is input to an inverter, and the inverter is controlled to generate the AC voltage of 230 V, or 240 V, when the internal combustion engine is in a normal operation state.
However, when using the generators having different winding specifications for the different voltage systems as described above, the two types of generators have to be prepared, thus inevitably increasing costs.
It can be considered that a generator having the same winding specifications is used to obtain both the 100 V system rated voltage and the 200 V system rated voltage by controlling the inverter, but such a construction requires a generator having a maximum output larger than a rated output of the inverter, thus increasing sizes of an armature core and an armature coil to increase sizes of a rotating electric machine.
In the inverter generator, it is preferable to use a generator having a maximum output suitable for a rated output of an inverter in order to prevent increase in a size of the generator more than necessary.
Therefore, an object of the invention is to provide a starter generator for an internal combustion engine that are adapted to obtain a 100 V system voltage and a 200 V system voltage, without increasing sizes of a rotating electric machine more than necessary.
The present invention is applied to a starter generator for an internal combustion engine that operates as an electric motor for starting the internal combustion engine when the internal combustion engine is started, and operates as a generator after the internal combustion engine is started.
According to the invention, the starter generator for an internal combustion engine includes: a magnet rotor mounted to a crankshaft of the internal combustion engine; a stator having a polyphase first armature coil and a polyphase second armature coil; a first battery and a second battery; a first driver provided between the first armature coil and the first battery, and a second driver provided between the second armature coil and the second battery; an inverter that converts a voltage of the first battery and a voltage of the second battery to an AC voltage; and a controller that controls the first driver, the second driver, and the inverter.
Each driver includes: a polyphase rectifier circuit that is constituted by a bridge circuit of diodes, and rectifies an AC voltage induced in the corresponding armature coil to supply the AC voltage to the corresponding battery; and a polyphase switch circuit that is constituted by a bridge circuit of switch elements, each switch element being connected in anti-parallel to the corresponding diode that forms the polyphase rectifier circuit.
The controller includes: a driver control unit that flows drive currents through the first armature coil and the second armature coil from the first battery and the second battery through the polyphase switch circuits in the first driver and the second driver, respectively, so as to rotate the magnet rotor in a direction of starting the internal combustion engine, when the internal combustion engine is started, and controls the polyphase switch circuits in the first driver and the second driver, so as to keep, at a value equal to or less than a set value, DC voltages supplied to the first battery and the second battery from the first armature coil and the second armature coil through the polyphase rectifier circuits in the first driver and the second driver, after the internal combustion engine is started; and an inverter control unit that controls the inverter so as to output an AC voltage at a desired frequency from the inverter.
The first battery and the second battery are connected in series or in parallel according to an effective value of the AC voltage output from the inverter and are connected between DC input terminals of the inverter.
With the construction as described above, the drive currents can be flowed through the first armature coil and the second armature coil from the first battery and the second battery through the switch circuits in the first driver circuit and the second driver circuit to drive the magnet rotor in the direction of starting the engine, when the internal combustion engine is started.
After the internal combustion engine is started, charging currents can be supplied to the first battery and the second battery from the first armature coil and the second armature coil through the rectifier circuits in the first driver and the second driver to charge the batteries, and output voltages of the batteries can be converted by the inverter into an AC voltage at a commercial frequency and supplied to a load.
As described above, the first battery and the second battery, connected in series or in parallel according to the effective value of the AC voltage output from the inverter, are connected between the input terminals of the inverter. Thus, the generator having a maximum output equal to a rated output of the inverter can be used to generate a 100 V system voltage and a 200 V system voltage. Therefore, a starter generator that can generate the 100 V system voltage and the 200 V system voltage can be obtained without increasing sizes of an armature core and the armature coils more than necessary.
In a preferable aspect of the invention, there are further provided a first diode having a cathode and an anode connected to a positive terminal of the first battery and a positive terminal of the second battery, respectively, and a second diode having a cathode and an anode connected to a negative terminal of the first battery and a negative terminal of the second battery, respectively, and the positive terminal of the first battery and the negative terminal of the second battery are connected to a positive DC input terminal and a negative DC input terminal, respectively, of the inverter.
With such a construction, the negative terminal of the first battery and the positive terminal of the second battery are connected or disconnected to transfer between a state where the first battery and the second battery are connected in series and a state where the both batteries are connected in parallel.
When the first diode and the second diode are provided as described above, it is preferable to connect a series-parallel transfer switch between the negative terminal of the first battery and the positive terminal of the second battery. With the series-parallel transfer switch, the transfer switch is turned on to connect the first battery and the second battery in series, and the transfer switch is turned off to connect the batteries in parallel.